The title compound, {[K(C₅H₉N₂O₇P₂)(H₂O)]·H₂O}_n, is polymeric and consists of layers parallel to (001) interconnected by hydrogen-bonding and π–π interactions. The K⁺ cation is eightfold coordinated in a KO₈ environment by O atoms from three different chelating zoledronate units and two coordinated water molecules. The zoledronate group presents its usual zwitterionic character, with negative charges in the singly protonated phosphonate groups and a positive charge at the protonated imidazole N atom. The anion binds to three different K⁺ cations in a (so far unreported) triply chelating manner. Intra- and interplanar interactions are enhanced by a variety of hydrogen bonds involving all available O–H and N–H donors. A strong imidazole-phosphonate C–H⋯O interaction is present in the structure.